This invention is related to cathode ray tubes, and is particularly concerned with method and means for cleansing cathode ray tubes during manufacture.
The manufacturing environment wherein the unsealed cathode ray tube envelopes are processed is commonly replete with contaminants, specifically particulate matter meeting the definition of "detritus." The contaminants are primarily those directly associated with cathode ray tube manufacture, such as particles of metal and metal oxides abraded from the shadow mask and the attaching members, particles of graphite dislodged from the conductive coating deposited on the inner surface of the funnel, particles of aluminum and of the lacquer used in the aluminizing process, and particles of phosphor from the imaging screen. The particles may range in size from one micron to several hundred microns.
Much effort has been directed to the cleansing of the interior of cathode ray tube envelopes during manufacture to rid CRT interiors of such contaminants. The neck of the tube is particularly critical area in that it encloses the electron gun, or guns in plural-beam tubes. If the inner surface of the neck is not immaculately clean, particulate matter present in the neck area can migrate to the gun and lodge between the electrodes to become a point source for the initiation of inter-electrode arcing. When present between the neck wall and the gun, particles can create a path for arcing between the gun and the neck; the resulting arc can be so severe as to crack the neck or vaporize gun parts. Further, particulate matter can attain a high velocity under the urging of electromagnetic fields adjacent to the gun and bombard sensitive gun parts such as the cathodes, resulting in cathode failure. Certain chemical particulates can, upon lodgement on a cathode, poison it and cause its early failure as an emitter of electrons.
So it is imperative that the cathode ray tube interior, and particularly the area within the neck, be thoroughly cleaned.
It is common in the manufacturing process to attempt to clean the cathode ray tube neck by "dipping," wherein the neck section is immersed in an ultrasonically vibrated cleaning solution, after which the tube is drip-dried. This means has proved only marginally adequate. Another means in common use is the use of an "auger," wherein a tool resembling a revolving bottle brush is inserted into the neck. Many of the particles dislodged by this means are pushed up further into the neck by the auger, and end up in a ring near the intersection of the neck and the funnel of the envelope. Sooner or later during the operating life of the tube, particles in the ring will be dislodged by shock or vibration or by electromagnetic forces, and become migrant to the detriment of tube operation.